Molecular and crystalline structure of furfural diacetate nitration intermediate

X-ray crystallography established the structure of the acetyl nitrate adduct to furfural diacetate (H. Gilman and G.F. Wright (1930)) as trans-2-acetoxy-5-nitro-2,5-dihydro-2-furfural diacetate (1a). The furanoid ring is essentially planar, its geometry being similar to that of 2,5-dihydrofuran molecule, except for the interatomic distance C(3)-C(4) which is shorter than the corresponding length of double C-C bond in alkenes. The C(5)-N 1.52 Å bond significantly exceeds the standard C-N bond lengths in nitroalkanes and nitrobenzene.     

The composition and structure of polyvinyl butyral furfural: NMR study

With the use of ¹H NMR, ¹³C NMR and two-dimensional NMR spectroscopy, the composition and structure of polyvinyl butyral furfural samples obtained at different stages of poly(vinyl alcohol) acetalization have been determined. The structure of low-molecular-mass and oligomer admixtures that may be formed in the course of synthesis of the copolymer or during its dissolution in alcohol has been estimated via one-dimensional and two-dimensional diffusion NMR spectroscopy.     

Nitration of furan derivatives with acetyl nitrate. Investigation of the products of nitration of furfural and furfural diacetate

It was established that 5-nitro-2-acetoxy-2,5-dihydro-, 5-nitro-4-acetoxy-4,5-dihydro-, and 5-nitrofurfural diacetates and 5-nitrofurfural are formed in the nitration of furfural and furfural diacetate in acetic anhydride. 2,5-Diacetoxy-2,5-dihydro- and 4,5-diacetoxy-4,5-dihydrofurfural diacetate are present in small amounts in the nitration products. 5-Nitrofurfural and 5-nitrofurfural diacetate are formed as a result of direct electrophilic substitution of hydrogen by a nitro group.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 601–606, May, 1976.     

In situ NMR spectroelectrochemistry for the structure elucidation of unstable intermediate metabolites

In situ NMR spectroelectrochemistry is presented in this study as a useful hybrid technique for the chemical structure elucidation of unstable intermediate species. An experimental setting was designed to follow the reaction in real time during the experimental electrochemical process. The analysis of ¹H NMR spectra recorded in situ permitted us (1) to elucidate the reaction pathway of the electrochemical oxidation of phenacetin and (2) to reveal the quinone imine as a reactive intermediate species without using any trapping reaction. Phenacetin has been considered as hepatotoxic at high therapeutic amounts, which is why it was chosen as a model to prove the applicability of the analytical method. The use of 1D and 2D NMR experiments led to the elucidation of the major species produced from the oxidation process. We demonstrated that in situ NMR spectroelectrochemistry constitutes a fast way for monitoring unstable quinone imines and elucidating their chemical structures.

NMR study of the spatial structure of synthetic pyrethroids

The spatial isomers of the new synthetic analogs of ethyl permithrinic ether and permethrin were investigated by NMR (¹H, ¹³C, DEPT (distortionless enhancement by polarization transfer), COSY (correlation spectroscopy), CHCORR (heteronuclear (C, H) shift correlation spectroscopy), ROESY (rotating-frame Overhauser effect spectroscopy)). Several tendencies were revealed in the ¹H and ¹³C chemical shifts of the α atoms of the substituents in the 2nd and 3rd positions of the cyclopropane ring. For substituents cis-orientated relative to the ester group, the spectra show a paramagnetic shift of the ¹H signals and the diamagnetic shift of the ¹³C signals relative to the trans-orientated substituents. The ¹H and ¹³C chemical shifts of the α atoms of the substituents in the 2nd and 3rd positions of the cyclopropane ring permit an unambiguous determination of the stereochemistry of ethyl permethrinic ether and permethrin analogs.     

A GLC and NMR analysis of the composition of polyvinyl butyral furfural acetal

Two procedures were suggested for separate determination of butyral and furfural acetal groups in polyvinyl butyral furfural acetal copolymer. The first procedure involves chromatographic determination of the volatile aldehydes after preliminary hydrolysis of the copolymer, in combination with chemical determination of the sum of acetal groups in the copolymer by oximation. The second procedure is based on NMR spectroscopy.     

Real-time NMR characterization of structure and dynamics in a transiently populated protein folding intermediate

Recent advances in NMR spectroscopy and the availability of high magnetic field strengths now offer the possibility to record real-time 3D NMR spectra of short-lived protein states, e.g., states that become transiently populated during protein folding. Here we present a strategy for obtaining sequential NMR assignments as well as atom-resolved information on structural and dynamic features within a folding intermediate of the amyloidogenic protein β2-microglobulin that has a half-lifetime of only 20 min.     

NMR study of the structure of a polyhydrate-forming ion exchanger

Institute of Inorganic Chemistry, Siberian Branch, Academy of Sciences of the USSR. Translated from Zhurnal Strukturnoi Khimii, Vol. 31, No. 3, pp. 39–43, May–June, 1990.     

Synthesis and structure analysis of cyclic furfural acetals

Quantum chemical calculations and the PMR method are used to show that the preferable conformation of cyclic furfural acetals is a chair with an axial orientation of the furyl substituent. In 2-(furyl-2′)-5-ethyl-5-oxymethyl-1,3-dioxane, the conformation equilibrium is shifted toward the transisomer with diaxial positions of the furyl and oxymethyl groups. The results of calculations suggest that the synthesis can lead to a cisisomer with an axial orientation of the furyl and equatorial oxymethyl groups. It was shown experimentally that the synthesis leads to a mixture of trans-and cis-isomers. Mild conditions (room temperature, aqueous medium) lead to formation of the transisomer and small amounts of the cisisomer (less than 2%). In rigid conditions (boiling in aromatic hydrocarbons), up to 20% of the cisisomer is formed. Translated fromZhurnal Struktumoi Khimii, Vol. 38, No. 6, pp. 1083–1091, November–December, 1997.     

The study of macromolecular structure by pulsed NMR

NMR has been widely used to determine chemical structure. The analysis of many important physical and physico-chemical properties such as molecular weight and mobility, the effect of crosslinking and entanglements and of solvents temperature, the role of crystalline regions and chain flexebility may be achieved very readily and simply these techniques. Once methods of analysis are understood and evaluated, they may serve only for the analysis of radiation effects but also for other forms of chemical treatment, the role of additives, orientation, and understanding and evaluation of important physical aspects, for which many of these polymers are intended. The use of pulsed NMR can also be used to evaluate radiation chemistry under different conditions, and it is expected that this knowledge could be extended to biological and medical systems, where a knowledge of the physical arrangements, mobility, entangled and other molecular properties and especially arrangement can be very important, yet difficult to measure.     

NMR spectral study of the structure of 2-amino-4-thiazolinones

As a consequence of partial double bond nature of the exocyclic C-N bond, 2-methylamino-4-thiazolinone exists in DMSO-D₆ as a mixture of E and Z conformers of the amino form with predominance of the sterically favored E conformer. 2-Phenylimino-4-thiazolidinone in the same solvent exists as a mixture of the E and Z isomers of the imino form.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 544–548, April, 1986.     

Nonnative interactions in the FF domain folding pathway from an atomic resolution structure of a sparsely populated intermediate: an NMR relaxation dispersion study

Several all-helical single-domain proteins have been shown to fold rapidly (microsecond time scale) to a compact intermediate state and subsequently rearrange more slowly to the native conformation. An understanding of this process has been hindered by difficulties in experimental studies of intermediates in cases where they are both low-populated and only transiently formed. One such example is provided by the on-pathway folding intermediate of the small four-helix bundle FF domain from HYPA/FBP11 that is populated at several percent with a millisecond lifetime at room temperature. Here we have studied the L24A mutant that has been shown previously to form nonnative interactions in the folding transition state. A suite of Carr-Purcell-Meiboom-Gill relaxation dispersion NMR experiments have been used to measure backbone chemical shifts and amide bond vector orientations of the invisible folding intermediate that form the input restraints in calculations of atomic resolution models of its structure. Despite the fact that the intermediate structure has many features that are similar to that of the native state, a set of nonnative contacts is observed that is even more extensive than noted previously for the wild-type (WT) folding intermediate. Such nonnative interactions, which must be broken prior to adoption of the native conformation, explain why the transition from the intermediate state to the native conformer (millisecond time scale) is significantly slower than from the unfolded ensemble to the intermediate and why the L24A mutant folds more slowly than the WT.     

An NMR study of the structure of hydrated fluorophosphatozirconates (hafnates)

³¹P, ¹⁹F, ¹H NMR is used to study fluorophosphatometalates of the composition MHfF₂PO₄·0.5H₂O (M = Rb, Cs) and CsMe₂F₆PO₄·4H₂O (Me = Zr, Hf). The data obtained indicate the isostructurality of compounds in each of these two groups. The lines in the NMR spectra are assigned. Assumptions about the character of the bond of PO₄ groups and F atoms with Me are made and schemes of the crystal structure of fluorophosphatometalates are proposed. The occurrence of several types of crystallization water characterized by different bond strengths and energy barriers of the diffusion motion is found.     

NMR 13C study of the structure of polyethyleneimine

The NMR ¹³C (CMR) spectrum of high molecular weight (M = 20,000) branched polyethyleneimine (PEI) obtained by polymerization of ethyleneimine (EI) in aqueous and alcoholic solutions at 50° with 1,3-dichloropropanol as initiator, contains 8 lines. The lines were identified using CMR spectra of model compounds, i.e. linear PEI, regularly branched PEI, diethylenetriamine and ethyleneimine pentamer. It has been shown that the deshielding effect of the nitrogen atoms on the α-atoms of carbon decreases in the folowing order: N_tert > N_sec > N_prim; with the atoms of carbon in the β-position, the effect increases in the opposite order.A quantitative estimation has been made of the distribution of the diads of elementary units containing the same and different nitrogen atoms. The data have been used to draw some conclusions about the structure of the PEI macromolecule.     

NMR study of the structure of poly(N-benzoyl-8-octanelactam)

The structure of a polymer prepared by the polymerization of N-benzoyl-8-octanelactam initiated with benzoic acid was studied by ¹H and ¹³C NMR, using S-INEPT, COSY, COLOC, and ROSEY methods, with the aid of model oligomers. Beside the expected N-benzoylated segments, the polymer also contained deacylated segments and about 50% of branching units. The polymer can be characterized as a statistical, highly branched copolymer of N-benzoyl-8-octanelactam and 8-octanelactam. © 1993 John Wiley & Sons, Inc.     

Clathrate tetraldehyde cavitand: single-crystal structure and NMR study

The tetraldehyde cavitand, C₁₀₀H₈₈O₂₀, was synthesised as the penultimate stage of a procedure to obtain cavitand-capped porphyrins. The complete structural characterisation was performed by single-crystal X-ray diffraction studies, NMR and IR spectroscopy. The inclusion phenomena of the solvent molecules were confirmed using NMR spectroscopy. The structure is the first example of a clathrate having an aromatic tetraldehyde cavitand grown as a single crystal with acetonitrile at the lower rim of the molecule and methanol at the upper rim of the molecule.     

NMR cryoporometry to study the fiber wall structure and the effect of drying

NMR cryoporometry has been used for investigating the porosity changes of bleached wood pulp upon drying. This NMR method follows the same principles as thermoporosimetry, which has been used for the same purpose during the last decade and makes it possible to investigate porous material in the water-swollen state. In this study bleached softwood kraft pulp was exposed to a series of drying procedures where the decrease in porosity within the fiber cell wall could be characterized for pore radii below 100 nm. This decrease in porosity is called hornification, which is an irreversible collapse of the fiber wall structure during drying and results in decreased uptake of water and reduced swelling of the fiber upon rewetting. Our results have been compared to the traditionally used water retention value (WRV) and correlates well with these. Furthermore, this NMR method could show the reduction of hornification when adsorbing the hemicellulose glucuronoxylan to the fiber.     

NMR study of methane + ethane structure I hydrate decomposition

The thermally activated decomposition of methane + ethane structure I hydrate was studied with use of 13C magic-angle spinning (MAS) NMR as a function of composition and temperature. The observed higher decomposition rate of large sI cages initially filled with ethane gas can be described in terms of a model where a distribution of sI unit cells exists such that a particular unit cell contains zero, one, or two methane molecules in the unit cell; this distribution of unit cells is combined to form the observed equilibrium composition. In this model, unit cells with zero methane molecules are the least stable and decompose more rapidly than those populated with one or two methane molecules leading to the observed overall faster decomposition rate of the large cages containing ethane molecules.